Stark-shifted image potential states of benzene bilayers on Cu(1 1 0) and Cu(1 1 1)

Benzene bilayer islands were observed by STM to be structurally similar on both Cu(1 1 1) and Cu(1 1 0) surfaces. The local electronic structure of the bilayers was studied using tunneling spectroscopy of Stark-shifted image potential states. On both Cu substrates, the n = 1 bilayer state was locally shifted away from the Fermi level when compared to the n = 1 monolayer state. The Stark-shift due to the electric field of the STM tip was observed to be greater for the n = 1 bilayer state than the n = 1 monolayer state on Cu(1 1 1).